1. Field of the Invention
The present invention relates to a digital memory and, more particularly, to such a memory having an accurate reference signal.
2. Background of the Invention
Solid-state digital memories using charge transfer devices, such as CCD's (charge coupled devices), BBD's (bucket brigade devices) and MOS's (metal oxide semiconductor devices), are well known in the art. To read out such memories, a reference level signal is provided. Output data at a level above the reference level is read out as one type of data (for example, a digital "1") and at a level below the reference as another type of data (for example, a digital "0").
The output data obtained from such memories will match the input data only to the extent that the reference level is precisely controlled relative to the levels of the data. When operating conditions, such as the temperature of the memory device, change, the levels of the data can shift. When that happens, the reference level no longer has the same relation to the data levels and bit errors can occur in the output of the memory.